I have one client who has a big problem straightening his arms at the top when he does a bench press. He cannot lock out his arms at the top when I hand him the bar, and the whole chain seems to collapse. This is taking a toll on my lower back as the bar seems to fall down when I give it to him. Why can’t he straighten his arms? He can straighten his arms when dong lighter DB chest press.
You’ve presented a real challenge on this one! The fact that someone can straighten his elbows in the bench press with light dumbbells but not with a barbell makes no sense whatsoever. I’ve never heard of this before. More details are needed for a thorough answer, but let’s look at several key considerations.
You mention that lighter dumbbell “chest press” presents no problem. I’m going to assume you mean dumbbell bench press. Chest press usually refers to a machine (not free weight) version of the bench press performed seated rather than supine. It’s a bench press if the pressing action is done supine on a bench, regardless of barbell or dumbbells.
Does your client grip the dumbbells similarly to the barbell?
If your client can successfully and completely extend the elbows with the hands overhead or in front of the chest as you indicate, you can probably rule out structural problems with the elbows as the culprit.
For people with an extensive history of bench pressing, especially without adequate flexibility training, an inability to straighten their elbows with the bar overhead (as in a press or jerk) is common. The problem is usually related to inflexibility in the shoulders and/or upper back. You’ve presented nothing to indicate your client suffers from excessive hypertrophy. Even with excessive hypertrophy, this should not affect the bench press.
It is not unusual to encounter people who think the bench press involves a rapid barbell descent, resulting in a bounce off the chest. While this is totally wrong, it is a fairly common occurrence. Does your client have a good understanding of the eccentric phase of the bench press? Can he hold any weight in position with his elbows fully extended? What is his explanation for why he cannot straighten his elbows and slowly lower the bar? Does he report any pain at any time throughout the exercise?
A similar muscular action is the push up. Can your client successful hold himself in an elbows-extended push up posture? If so, how does he perform push ups? Is there a rapid drop to the ground, as if he cannot descend under control?
If your client can’t lower, under control, a barbell in the bench press or himself in a push up, it would seem impossible for him to perform the concentric portion of the lift properly either. I’ll guess that your spotting does not include your helping him lift the bar. If your client cannot successfully straighten his arms in the bench press, regardless of weight, I’d be tempted to avoid doing bench presses. Certainly there’s no need for you to include an exercise that potentially causes you, the spotter, an injury.
You may wish to enlist the services of a good physical therapist who can evaluate your client for injury or muscle imbalance problems.